Dry-type rubber pressing apparatus

ABSTRACT

Powder is filled in an axially elongate powder filling space defiined in a flexible pressure tube, and the pressure-bearing surface of the flexible pressure tube is pressurized with a pressurizing fluid, from a wall portion of the pressure tube which corresponds to a localized region of the powder filling space progressively toward another wall portion of the pressure tube which corresponds to an end of the powder filling space, until the pressure-bearing surface of the pressure tube is pressurized in its entirety, thereby compacting the powder in the powder filling space. Therefore, air in the powder is progressively squeezed toward the end of the powder filling space where the air can be discharged. Thus, no air remains trapped in the powder, and a formed product is prevented from being damaged, which enables elongate products to be produced.

This application is a Divisional of Application Ser. No. 57,388, filedJune 2, 1987.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dry-type rubber pressing method andapparatus for forming powder into a product under hydrostatic pressureduring a dry-type process while squeezing air in the powder into an areawhich does not adversely affect the formed product during the pressingprocess.

2. Prior Art

FIG. 41 of the accompanying drawings illustrates a conventional dry-typehydrostatic rubber pressing apparatus. The apparatus includes a mold 2made of a flexible material such as neoprene rubber, urethane resin, orthe like and defining therein an axially elongate powder filling space1, a pair of lids 3, 1 covering the upper and lower open ends 1a, 1b ofthe powder filling space 1, a flexible pressure tube 5 fitted over themold 2, and a retainer case 6 fitted over the pressure tube 5, with anannular pressure chamber 8 defined between the pressure tube 5 and theretainer case 6. The retainer case 6 has liquid supply and dischargeports 6c, 6d opening into the pressure chamber 8. The retainer case 6has an axial through hole 6a extending vertically as shown, and thepressure tube 5 is disposed in the hole 6a. A core 9 is detachablydisposed between the upper and lower lids 3, 4 and extends verticallyand axially in the powder filling space 1. The core 9 has upper andlower bolt portions 9a, 9b extending through the lids 3, 4,respectively, with nuts 10, 11 tightened over the bolt portions 9a, 9b,respectively. The mold 2 covered with the upper and lower lids 3, 4 isinserted through the hole 6a into the pressure tube 5, and is retainedin place by clamps 12, 13 threaded, respectively, in upper and loweropenings 6e, 6f defined in the retainer case 6.

The operation of the conventional dry-type rubber pressing apparatusthus constructed will be described below. The upper clamp 12 is detachedfrom the retainer case 6, and the mold 2 is taken out of the retainercase 6. The upper nut 10 and the lid 3 are then removed from the mold 2,and the powder filling space 1 is filled with a mass of powder 14.Thereafter, the upper end of the powder filling space 1 filled with thepowder 14 is closed by the lid 3, and the nut 10 is tightened over thebolt portion 9a of the core 9. The mold 2 is then inserted through thehole 6a into the pressure tube 5, the clamp 12 is then threaded to theretainer case 6 in opening 6e, whereupon the preparatory process iscompleted. Then, the pressure chamber 8 defined between the retainercase 6 and the pressure tube 5 is supplied with a liquid 7 underpressure through the liquid supply and discharge ports 6c, 6d. As theliquid 7 under pressure is supplied, the flexible pressure tube 5 ispressed against substantially the entire outer surface 2a of the mold 2simultaneously, although not specifically shown. Under the radiallyinward pressure from the pressure tube 5, the flexible mold 2 has itsinside diameter D reduced to simultaneously pressurize the entire columnof powder 14 in the powder filling space 1. The pressure of air presentin the powder 14 is increased as the pressure of the liquid 7 increases.Therefore, the air passes through minute air passages between the powderparticles toward the lids 3, 4, and is discharged through the threadgaps between the bolt portions 9a, 9b and the nuts 10, 11. After thepressurization is performed over a prescribed time, the pressure liquid7 is discharged from the pressure chamber 8 through the liquid supplyand discharge ports 6c, 6d. As the pressure of the liquid 7 is reduced,the flexible mold 2 and the pressure tube 5 resiliently return to theiroriginal shape until the original inside diameter D of the mold 2 isreached. Then, the upper clamp 12 is detached from the retainer case 6and the mold 2 is removed from the retainer case 6. Finally, the formedproduct (not shown) in the mold 2 and the mold 2 and the core 9 areseparated from each other.

As described above, the pressure of air in the powder 14 is increased asthe pressure of the liquid 7 is increased, and the air flows through theair passages between the powder particles toward the lids 3, 4 and isdischarged out through the gaps between the bolt portions 9a, 9b and thenuts 10, 11. In order to discharge the air in the powder 14 quickly, itis necessary that the air pressure be high and the air passages definedas continuous gaps between the powder particles be large. To increasethe air pressure, the pressure of the liquid 7 should be increased. Asthe powder 14 is pressurized, however, the air passages defined ascontinuous gaps between the powder particles are greatly reduced orclosed. Accordingly, increasing the air pressure and enlarging the airpassages are contradictory to each other.

In the conventional dry-type rubber pressing method and apparatus, asthe liquid 7 under pressure is supplied, the overall pressurizing regionin the mold 2 is substantially simultaneously pressed to reduce theinside diameter D of the mold 2. As a consequence, the pressure of theair in the powder 14 is increased and at the same time the gaps betweenthe powder particles are reduced or closed throughout the entire powderfilling space 1. Therefore, the above contradictory problem cannot beresolved, and the following drawbacks are caused: Where the longitudinaldimension H of the powder filling space 1 is increased, the aircompressed under high pressure in the powder 14 filled centrally in thepowder filling space 1 cannot be removed completely since the distanceto the air-discharging gaps defined between the bolt portions 9a, 9b andthe nuts 10, 11 is large, with the result that compressed air remainstrapped in the formed product. The air trapped in the formed producttends to be expanded to damage the product when the pressure of theliquid 7 is reduced. To prevent compressed air from remaining in theproduct, it has been necessary for the longitudinal dimension H of thepowder filling space 1 in the conventional dry-type rubber pressingmethod and apparatus to be 500 mm or less. This is disadvantageous inthat longer products cannot be produced.

SUMMARY OF THE INVENTION

In view of the aforesaid shortcomings of the conventional dry-typerubber pressing method and apparatus, it is an object of the presentinvention to provide a dry-type rubber pressing method and apparatuscapable of producing elongate and high-quality molded products whilepreventing compressed air from being trapped therein.

According to the present invention, a flexible pressure tube with anaxially elongate powder filling space defined therein is squeezed in alimited or localized region, and thereafter the squeezed region isprogressively expanded toward a portion of the pressure tube whichcorresponds to an end of the powder filling space thereby pressurizingthe entire pressure-bearing surface of the pressure tube.

During the pressing process, air in the powder in the powder fillingspace is squeezed into an area which does not adversely affect theformed product, so that no compressed air is trapped in the product.

With the present invention, elongate and high-quality products whichhave conventionally been unable to be produced can be formed byperforming the above processing steps.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which preferredembodiments of the present invention are shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional view of a dry-type rubberpressing apparatus according to a first embodiment of the presentinvention;

FIG. 2 is a transverse cross-sectional view taken along line II--II ofFIG. 1;

FIGS. 3(A) and 3(B) are enlarged fragmentary longitudinalcross-sectional views showing an initial pressurizing state in theapparatus of FIG. 1;

FIG. 4 is a longitudinal cross-sectional view showing a finalpressurizing state in the apparatus of FIG. 1;

FIG. 5 is a longitudinal cross-sectional view showing the manner inwhich a formed product is removed from the apparatus of FIG. 1;

FIG. 6 is a fragmentary longitudinal cross-sectional view of a dry-typerubber pressing apparatus according to a second embodiment of thepresent invention, the view also illustrating a system for supplying anddischarging a pressurizing liquid and a system for discharging a liquid;

FIG. 7 is a longitudinal cross-sectional view of a dry-type rubberpressing apparatus according to a third embodiment of the presentinvention;

FIG. 8 is an enlarged fragmentary cross-sectional view of a sealstructure in a pressure tube in the apparatus of FIG. 7;

FIG. 9(A) is an enlarged fragmentary cross-sectional view of anotherseal structure while not pressurized;

FIG. 9(B) is a view similar to FIG. 9(A), showing the seal structure ofFIG. 9(A) while pressurized;

FIG. 10(A) is an enlarged fragmentary cross-sectional view of stillanother seal structure while not pressurized;

FIG. 10(B) is a view similar to FIG. 10(A), showing the seal structureof FIG. 10(A) while pressurized;

FIG. 11 is a longitudinal cross-sectional view of a dry-type rubberpressing apparatus according to a fourth embodiment of the presentinvention;

FIG. 12 is a transverse cross-sectional view taken along line XII--XIIof FIG. 11;

FIG. 13 is a longitudinal cross-sectional view of a dry-type rubberpressing apparatus according to a fifth embodiment of the presentinvention;

FIG. 14 is a longitudinal cross-sectional view of a dry-type rubberpressing apparatus according to a sixth embodiment of the presentinvention;

FIG. 15 is a transverse cross-sectional view taken along line XV--XV ofFIG. 14;

FIGS. 16(A) and 16(B) are enlarged fragmentary longitudinalcross-sectional views showing a pressurizing state in the apparatus ofFIG. 14;

FIG. 17 is a longitudinal cross-sectional view of the apparatus of FIG.14, showing a pressurizing state;

FIG. 18 is a longitudinal cross-sectional view showing the manner inwhich a formed product is removed from the apparatus of FIG. 14;

FIG. 19 is a longitudinal cross-sectional view of a dry-type rubberpressing apparatus according to a seventh embodiment of the presentinvention;

FIG. 20 is a longitudinal cross-sectional view of a dry-type rubberpressing apparatus according to an eighth embodiment of the presentinvention;

FIG. 21 is a transverse cross-sectional view taken along line IIXl--IIXIof FIG. 20;

FIGS. 22(A) and 22(B) are enlarged fragmentary longitudinalcross-sectional views showing a pressurizing state in the apparatus ofFIG. 20;

FIG. 23 is a longitudinal cross-sectional view of the apparatus of FIG.20, showing a pressurizing state;

FIG. 24 is a longitudinal cross-sectional view showing the manner inwhich a formed product is removed from the apparatus of FIG. 20;

FIG. 25 is a longitudinal cross-sectional view of a dry-type rubberpressing apparatus according to a ninth embodiment of the presentinvention;

FIG. 26 is an enlarged fragmentary cross-sectional view of a sealstructure in a pressure tube in the apparatus of FIG. 25;

FIG. 27(A) is an enlarged fragmentary cross-sectional view of anotherseal structure while not pressurized;

FIG. 27(B) is a view similar to FIG. 27(A), showing the seal structureof FIG. 27(A) while pressurized;

FIG. 28(A) is an enlarged fragmentary cross-sectional view of stillanother seal structure while not pressurized;

FIG. 28(B) is a view similar to FIG. 28(A), showing the seal structureof FIG. 28(A) while pressurized;

FIG. 29 is a longitudinal cross-sectional view of a dry-type rubberpressing apparatus according to a tenth embodiment of the presentinvention;

FIG. 30 is a longitudinal cross-sectional view of a dry-type rubberpressing apparatus according to an eleventh embodiment of the presentinvention;

FIG. 31 is a transverse cross-sectional view taken along lineIIIXl--IIIXI of FIG. 30;

FIG. 32 is an enlarged fragmentary longitudinal cross-sectional viewshowing another embodiment of a backup tube;

FIGS. 33(A) and 33(B) are enlarged fragmentary longitudinalcross-sectional views showing a pressurizing state;

FIG. 34 is a longitudinal cross-sectional view of the apparatus of FIG.30, showing a pressurizing state;

FIG. 35 is a longitudinal cross-sectional view showing the manner inwhich a formed product is removed from the apparatus of FIG. 30;

FIG. 36 is a longitudinal cross-sectional view of a dry-type rubberpressing apparatus according to a twelfth embodiment of the presentinvention;

FIG. 37 is a longitudinal cross-sectional view of a dry-type rubberpressing apparatus according to a thirteenth embodiment of the presentinvention;

FIG. 38 is a longitudinal cross-sectional view of a dry-type rubberpressing apparatus according to a fourteenth embodiment of the presentinvention;

FIG. 39 is an enlarged fragmentary longitudinal cross-sectional view ofa pressure chamber in the apparatus of FIG. 38;

FIG. 40 is a graph showing the application of a maximum formingpressure; and

FIG. 41 is a longitudinal cross-sectional view of a conventionaldry-type rubber pressing apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 1st Embodiment

FIGS. 1 through 5 show a dry-type rubber pressing apparatus according toa first embodiment of the present invention. The apparatus, generallydesignated by the reference numeral 20, essentially comprises a pressedassembly 21 and a pressing assembly 22.

The pressed assembly 21 is conventional and includes a flexible mold 2defining therein a vertically elongate powder filling space 1, a pair oflids 3, 4 covering the upper and lower open ends 1a, 1b of the powderfilling space 1, a core 9 extending between the upper and lower lids 3,4, and nuts 10, 11 threaded respectively over bolt portions 9a, 9b ofthe core 9. The core 9 may be have a circular, elliptical, polygonal, orother suitable transvere cross-sectional shape, and one or more cores 9may be employed. When a solid product is to be formed, the core 9 is notdisposed in the mold 2.

The pressing assembly 22 of the apparatus 20 has an improved structure.The pressing assembly 22 includes a pressure tube 25 fitted in aretainer case 26. The retainer case 26 comprises a rigid outer tube 23,an inner tube 24 backing up the pressure tube 25, and a pair of upperand lower lids 28, 29 threaded over the upper and lower ends,respectively, of the outer tube 23 and sandwiching the pressure tube 25.An annular pressure chamber 27 is defined between the outer tube 23 andthe inner tube 24. The pressure tube 25 is made of a flexible materialsuch as neoprene rubber, urethane resin, or the like and has a rubberhardness in the range of 40 to 90 according to Japan Industrial Standard(JIS). The pressure tube 25 has an outer peripheral surface 25a servingas a pressure bearing surface for bearing the pressure exerted by apressurizing liquid 7. The outer peripheral surface 25a includes aninitial pressurizing region 25a-1 remotest from the ends 1a, 1b of thepowder filling space 1. The inner tube 24 has an inner liquid guidesurface 26f held in intimate contact with the outer peripheral surface25a of the pressure tube 25. The inner tube 24 has a plurality ofradially extending liquid supply ports 26c (FIG. 2), open at the innerliquid guide surface 26f, confronting the initial pressurizing region25a-1 and communicating with the pressure chamber 27. A suitable numberof liquid supply and discharge ports 26g extend radially through theinner tube 24 adjacent the upper end of the liquid guide surface 26f andare in communication with the pressure chamber 27, the liquid supply anddischarge ports 26g being disposed in a radially confronting relation tothe lid 3 through the pressure tube 25. A suitable number of liquidsupply and discharge ports 26h also extend radially through the innertube 24 adjacent the lower end of the liquid guide surface 26f and arein communication with the pressure chamber 27, the liquid supply anddischarge ports 26h being disposed in a radially confronting relation tothe lid 4 through the pressure tube 25. The upper and lower liquidsupply and discharge ports 26g, 26h are provided to discharge airpresent between the liquid guide surface 26f and the pressure tube 25,and are normally closed off by the outer peripheral surface 25a of thepressure tube 25. Portions 25c, 25d of the pressure tube 25 which closethe liquid supply and discharge ports 26g, 26h are radially backed bythe lids 3, 4 of the pressed assembly 21, so that the liquid supply anddischarge ports 26g, 26h remain closed until these portions 25c, 25d areflexibly deformed (FIG. 4). The outer tube 23 has liquid supply anddischarge ports 23a, 23b defined in the vicinity of upper and lower endsthereof and are open to the pressure chamber 27. The liquid supply anddischarge ports 23a, 23b are coupled to liquid supply and dischargepipes of a liquid supply and discharge system (not shown).

The initial pressurizing region 25a-1 of the outer peripheral surface25a of the pressure tube 25 is not limited to the illustrated centralposition, but may be located at a suitable localized region between theupper and lower ends 25e, 25f of the pressure tube 25.

In the illustrated embodiment, the longitudinal axis of the powderfilling space 1 is shown as extending vertically. However, thelongitudinal axis of the powder filling space 1 may be inclined orhorizontal.

Operation of the apparatus 20, or the method of the present invention,will be described below. As shown in FIGS. 1 and 2, the pressed assembly21 is provided with a mass of powder 14 in the powder filling space 1.The pressed assembly 21 is then inserted into the pressing assembly 22,and held in position by upper and lower clamps 12, 13 threaded in thepressing assembly 22. Then, a pressurizing liquid 7 (such as oil,glycerin, an aqueous solution of boric acid, or the like) which issupplied under pressure from the liquid supply and discharge systemflows through the liquid supply and discharge ports 23a, 23b of theouter tube 23 into the pressure chamber 27. When the pressure of theliquid 7 in the pressure chamber 27 reaches a prescribed level (forexample in the range of 50 to 200 kg/cm²), the liquid 7 flows throughthe liquid supply ports 26c toward the pressure tube 25 and flowsbetween the outer peripheral surface 25a of the pressure tube 25 and theliquid guide surface 26f. Since the liquid supply and discharge ports26g, 26h defined adjacent the upper and lower ends of the inner tube 24are closed by the portions 25c, 25d of the pressure tube 25, the liquid7 under pressure does not flow out past the pressure tube 25. As shownin FIG. 3(A), the liquid 7 when under low pressure is applied to theinitial pressurizing region 25a-1 of the outer peripheral surface 25aconfronting the liquid supply and discharge port 26c and elasticallyexpands the apparatus at the initial pressurizing region 25a-1 radiallyinwardly. The mold 2 is now pressed only at a portion of its outerperipheral surface 2a which faces the initial pressurizing region 25a-1,reducing the inside diameter D of the mold 2 to compact the powder 14.The pressure of air (not shown) in the pressurized powder 14 isincreased and the air quickly flows into air passages defined by gapsbetween powder particles which are not compacted. Therefore, no airremains under compression in the pressurized powder 14. As the amount ofsupplied liquid 7 increases, it flows into successive pressurizingregions adjacent to the initial pressurizing region 25a-1 andprogressively expands the apparatus at those successive pressurizingregions radially inwardly. The powder 14 filled in the powder fillingspace 1 is thus progressively compacted from the region in the powderfilling space 1 which confronts the initial pressurizing region 25a-1toward the ends 1a, 1b (see FIG. 1) of the powder filling space 1. Asthe powder 14 is axially progressively pressurized or compacted, airpresent in the powder 14 in the powder filling space 1 is squeezed fromthe region in the powder filling space 1 which confronts the initialpressurizing region 25a-1 toward the ends 1a, 1b of the powder fillingspace 1, and is finally discharged out of the powder filling space 1through the thread gaps defined between the bolt portions 9a, 9b of thecore 9 and the nuts 10, 11. As a consequence, air under compressionwhich would damage a formed product A (FIG. 5) is prevented from beingtrapped in the compacted powder 14. The liquid 7 under pressure suppliedbetween the entire outer peripheral surface 25a and the liquid guidesurface 26f is pressurized up to a prescribed final pressure level (forexample, in the range of 500 to 5,000 kg/cm²), to compact the powder 14,as shown in FIG. 4. After the pressurization is performed over aprescribed period of time, the pressure of the liquid 7 in the pressurechamber 27 is reduced. As the pressure of the liquid 7 is lowered, theflexible mold 2 and the pressure tube 25 return to their original shapeunder their own resiliency until the original inside diameter D of themold 2 is recovered, as shown in FIG. 5. After the upper clamp 12 hasbeen detached from the retainer case 26, the pressed assembly 21 ispulled out of the retainer case 26. Then, the nuts 10, 11 and the lids3, 4 are removed, and the formed product A, the core 9, and the mold 2are separated from each other.

2nd Embodiment

FIG. 6 shows an apparatus 30 according to a second embodiment of thepresent invention. The apparatus 30 is significantly different from theapparatus 20 of the first embodiment in that a pressure tube 25 isfitted in a rigid outer tube 33 constituting a retainer case 36. Theouter tube 33 has an inner peripheral liquid guide surface 36f facingthe outer peripheral surface 25a of the pressure tube 25. The liquidguide surface 36f has defined therein an annular distribution groove 33dconfronting the entire periphery of an initial pressurizing region 25a-1of the pressure tube 25, an annular distribution groove 33e facing anupper portion of the outer peripheral surface 25a of the pressure tube25, and an annular distribution groove 33f facing a lower portion of theouter peripheral surface 25a of the pressure tube 25. The distributiongrooves 33d, 33e, 33f communicate, respectively, with liquid supply anddischarge ports 33c, 33a, 33b defined in the outer tube 33.

A liquid supply and discharge system 40 for supplying and discharging aliquid 7 under pressure to and from the apparatus 30 will be describedbelow. An initial pressurizing pump 41 and a boost pump 42 have inletports 41a, 42a positioned in an oil tank 43. The initial pressurizingpump 41 has an outlet port 41b coupled via a check valve 44 and asolenoid-operated valve 45 to the liquid supply and discharge port 33cof the outer tube 33. Coupled between the outlet port 41b and the checkvalve 44 are a pressure switch 46 and a relief valve 47. The boost pump42 has an outlet port 42b coupled to an inlet port 48a of a boostcylinder 48 and a relief valve 50. The boost cylinder 48 has an outletport 48b connected via a check valve 51 to the solenoid-operated valve45. A pressure switch 52 is coupled between the outlet port 48b of theboost cylinder 48 and the check valve 51. The initial pressurizing pump41 and the boost pump 42 are started and stopped by a control circuit53. More specifically, the control circuit 53 operates the initialpressurizing pump 41 only until the pressure switch 46 produces adetected pressure setting signal indicative of an initial pressuresetting. In response to a detected pressure setting signal from thepressure switch 46, the control circuit 53 stops the operation of theinitial pressurizing pump 41, and starts the boost pump 42. The controlcircuit 53 also operates the boost pump 42 until the pressure switch 52generates a detected pressure setting signal indicative of a highpressure setting. When the control circuit 53 receives a detectedpressure setting signal from the pressure switch 52, the control circuit53 stops the operation of the boost pump 42. A drain pipe 63 leading tothe oil tank 43 is connected via a solenoid-operated valve 54 to theliquid supply and discharge port 33b of the outer tube 33 and also, viasolenoid-operated valves 55, 56, to the liquid supply and discharge port33a of the outer tube 33. The oil tank 43 is associated with a liquidlevel detector switch 57.

A liquid discharge system 64 serves to forcibly discharge the liquid 7under pressure which remains between the liquid guide surface 36f of theouter tube 33 and the outer peripheral surface 25a of the pressure tube25. The liquid discharge system 64 includes a compressed air source 58having an outlet port 58a connected through solenoid-operated valves 59,60 to a point between the solenoid-operated valves 55, 56. A muffler 62is joined via a solenoid-operated valve 61 between the solenoid-operatedvalves 59, 60. The outlet port of the muffler 62 should preferably beconnected to the oil tank 43 since it may discharge the liquid 7 underpressure.

Operation of the apparatus 30 according to the second embodiment willhereinafter be described with reference to operation of the liquidsupply and discharge system 40 and the liquid discharge system 64. Thepressed assembly 21 charged with the powder 14 is loaded into the outertube 33. The liquid supply and discharge system 40 closes thesolenoid-operated valves 54, 55, 56 and opens the solenoid-operatedvalve 45. The initial pressurizing pump 41 is started in response to anoutput signal from the control circuit 53 to supply the liquid 7 underpressure to the liquid supply and discharge port 33c of the outer tube33. The liquid 7 under pressure flows between the outer peripheralsurface 25a of the pressure tube 25 and the liquid guide surface 36f ofthe retainer case 36 to progressively compact the powder 14 filled inthe powder filling space 1 so that the powder is progressively squeezedfrom the region of the powder filling space 1 confronting the initialpressurizing area 25a-1 of the pressure tube 25 to the ends 1a, 1b ofthe powder filling space 1. Air in the powder 14 is thereforeprogressively squeezed toward the ends 1a, 1b of the powder fillingspace 1. Upon the completion of the initial pressurization of the entireamount of powder 14, the pressure of the liquid 7 discharged from theinitial pressurizing pump 41 is increased. In response to an increase inthe liquid pressure from the initial pressurizing pump 41, the pressureswitch 46 applies a detected pressure setting signal to the controlcircuit 53 to enable the same to stop the initial pressurizing pump 41and start the boost pump 42. The boost pump 42 then supplies the liquid7 under a high pressure (for example, ranging from 500 to 5,000 kg/cm²)between the outer peripheral surface 25a of the pressure tube 25 and theliquid guide surface 36f of the retainer case 36 to compact the powder14. When the high-pressure liquid 7 reaches a prescribed pressure level,the pressure switch 52 applies a detected pressure setting signal to thecontrol circuit 53 which then deactivates the boost pump 42. When agiven period of time elapses after the deactivation of the boost pump42, the solenoid-operated valve 45 is closed, and the solenoid-operatedvalves 54, 55, 56 are opened. Most of the liquid 7 under pressurepresent between the outer peripheral surface 25a and the liquid guidesurface 36f is now forced by elastic recovery of the pressure tube 25and the mold 2 to flow through the drain pipe 63 back into the oil tank43. The liquid level detector switch 57 in the oil tank 43 detects whenthe amount of the liquid 7 which has flowed back into the oil tank 43has reached a prescribed level. A slight amount of the liquid 7 underpressure may remain between the outer peripheral surface 25a and theliquid guide surface 36f due, for example, to the resistance of thedrain pipe. When such residual liquid is left, it causes the pressuretube 25 to keep on pressing the mold 2, making it difficult to pull themold 2 out of the pressure tube 25. The pressurizing liquid 7 is verylikely to remain between the outer peripheral surface 25a and the liquidguide surface 36f when the axial length of the pressure tube 25 islarge. The remaining liquid 7 can be forcibly discharged by the liquiddischarge system 64.

The liquid discharge system 64 operates as follows: Thesolenoid-operated valves 59, 60, 61 are closed in advance. In responseto a detected signal from the liquid level detector switch 57 in the oiltank 43, the solenoid-operated valve 56 is closed, and thesolenoid-operated valves 59, 60 are opened. Air under pressure suppliedfrom the compressed air source 58 flows through the solenoid-operatedvalves 60, 59, 55 and the liquid supply and discharge port 33a andbetween the outer peripheral surface 25a and the liquid guide surface36f to force out the remaining liquid 7. The liquid 7 is forced toquickly flow through the lower liquid supply and discharge port 33b, thesolenoid-operated valve 54, and the drain pipe 63 into the oil tank 43.After the liquid 7 has returned to the oil tank 43, thesolenoid-operated valve 60 is closed and the solenoid-operated valve 61is opened to discharge air remaining between the outer peripheralsurface 25a and the liquid guide surface 36f.

Upon the completion of the removal of any remaining liquid 7, thepressed assembly 21 is taken out of the pressure tube 25, after whichthe mold 2 and the molded product (not shown) are separated from eachother.

3rd Embodiment

FIGS. 7 and 8 show an apparatus 70 according to a third embodiment ofthe present invention. The apparatus 70 is different from the apparatus30 of the second embodiment (FIG. 6) in that seal structures 81, 82 areprovided near the upper and lower ends of a pressure tube 75, and aprotective tube 77 is interposed between the pressure tube 75 and themold 2.

As shown in FIG. 8, the seal structure 81 near the upper end of thepressure tube 75 includes an annular groove 85 defined in a lid 83. Thepressure tube 75 has an upper edge 75e extending in the annular groove85 and having an outer peripheral surface 75a with a seal ring groove 86defined therein. A seal ring 87 fitted in the seal ring groove 86 isheld in intimate contact with the inner peripheral surface 85a of theannular groove 85. The annular groove 85 has an innermost surface 85bserving as a backup portion for the upper edge 75e of the pressure tube5. The cross section of the seal ring 87 is not limited to an 0-shape,but may be a V-shape, an X-shape, or any of other suitable shape. Theseal structure 82 (FIG. 7) near the lower end of the pressure tube 75 isidentical to the seal structure 81 near the upper end.

The protective tube 77 is made of a flexible material such as neoprenerubber, urethane resin, or the like. The protective tube 77 protects thepressure tube 75 by holding the pressure tube 75 out of contact with thelids 3, 4 of the pressed assembly 21.

FIGS. 9(A) and 9(B) illustrate another seal structure which may bedisposed near each of the upper and lower ends of the pressure tube 75.The seal structure 91 includes an annular groove 85 defined in a lid 83.The pressure tube 75 has an upper edge 75e extending in the annulargroove 85 which has an inner peripheral surface 85a with a seal ringgroove 96 defined therein. A seal ring 97 extending in the seal ringgroove 96 is held in intimate contact with the upper edge 75e of thepressure tube 75. The annular groove 85 has an innermost surface 85bserving as a backup portion for the upper edge 75e of the pressure tube75.

FIGS. 10(A) and 10(B) show still other seal structures which may bedisposed near each of the upper and lower ends of the pressure tube 75.The seal structure 101 includes an annular groove 85 defined in a lid83. The pressure tube 75 has an upper edge 75e fitted in the annulargroove 85. Two confronting seal ring grooves 108, 109 are defined,respectively, in the outer peripheral surface 75a of the upper edge 75eand the inner peripheral surface 85a of the annular groove 85. Arespective seal ring 107 fitted in the seal ring grooves 108, 109 isheld in intimate contact with the bottoms 108a, 109a of the seal ringgrooves 108, 109. The annular groove 85 has an innermost surface 85bserving as a backup portion for the upper edge 75e of the pressure tube75.

4th Embodiment

FIGS. 11 and 12 show an apparatus 110 according to a fourth embodimentof the present invention. The apparatus 110 has a powder filling space 1defined by an inner peripheral surface 117j of a pressure tube 117.

5th Embodiment

FIG. 13 shows an apparatus 120 according to a fifth embodiment of thepresent invention. The apparatus 120 includes a mold 121 having a bottomand around which a pressure tube 127 is fitted. The pressure tube 127 isdisposed in a retainer case 126 having annular distribution grooves123e, 123f near the upper and lower ends of a liquid guide surface 126fon the inner periphery of the outer tube 123. The annular distributiongrooves 123e, 123f communicate, respectively, with liquid supply anddischarge ports 123a, 123b defined in the retainer case 126. The mold121 is covered with a lid 124 which may have an air discharge hole 124a.

The operation of the apparatus 120, or a method according to the presentinvention, will be described below. The flexible mold 121 with a mass ofpowder 14 filling space 1 is inserted into the flexible pressure tube127, and the upper opening of the mold 121 is closed by the lid 124. Thelid 124 is fastened in position by the clamp 12. Then, the pressurizingliquid 7 is supplied under pressure to the lower liquid supply anddischarge port 123b. The supplied liquid 7 pressurizes the outerperipheral surface 127b of the pressure tube 127 progressively upwardly.The mold 121 is then pressurized by the pressure tube 127 progressivelyupwardly. The powder 14 filled in the mold 121 is in turn pressurized orcompacted by the mold 121 progressively from the bottom 1b to upper end1a of the powder filling space 1. As the powder 14 is progressivelycompacted, air in the powder 14 is squeezed from the bottom region toupper end 1a of the powder filling space 1 and is then discharged outfrom the air discharge hole 124a of the lid 124. Where the lid 124 hasno air discharge hole 124a, air in the powder 14 is squeezed toward theupper end 1a of the powder filling space 1 where the air is separatedfrom the powder 14. As a consequence, the compacted powder 14 does notcontain compressed air which would damage a formed product. The liquid 7supplied between the entire outer peripheral surface 127a of thepressure tube 127 and the liquid guide surface 126f of the outer tube123 is pressurized up to a prescribed final pressure level to compactthe powder 14. Upon completion of the compaction of the powder over agiven period of time, the pressure of the liquid 7 is lowered. As thepressure of the liquid 7 is reduced, the flexible mold 121 and theflexible pressure tube 127 are allowed under their own resiliency torestore their original inside diameters. Finally, the lid 124 is removedfrom the mold 121, and a solid formed product (not shown) is separated.

6th Embodiment

FIGS. 14 through 18 show an apparatus 220 according to a sixthembodiment of the present invention, the apparatus 220 comprising apressed assembly 21 and a pressing assembly 22. The pressed assembly 21has the same structure as that of the first embodiment (FIG. 1).

As shown in FIG. 14, the pressing assembly 22 having an improvedstructure includes a pressure tube 225 fitted in a retainer case 226.The retainer case 226 comprises a rigid outer tube 223, an inner tube224 backing the pressure tube 225, and a pair of upper and lower lids229, 230 threaded over the upper and lower ends, respectively, of theouter tube 223 and sandwiching the pressure tube 225. An annularpressure chamber 228 is defined between the outer tube 223 and the innertube 224. The pressure tube 225 is made of a flexible material such asneoprene rubber, urethane resin, or the like and has a rubber hardnessin the range of 40 to 90 according to Japan Industrial Standard (JIS).The pressure tube 225 has an outer peripheral surface 225a having aplurality of annular grooves 225b defined at suitable intervals P(P=100-300 mm, for example) longitudinally along the outer peripheralsurface 225a, defining seven pressurizing regions 225a-1, 225a-2, ...225a-7. The central pressurizing region 225a-1 serves as an intialpressurizing region. Resilient seal rings 235 are disposed,respectively, in the annular grooves 225b with an interference fit. Thecross section of each of the resilient seal rings 235 is not limited toan 0-shape, but may be a V-shape, an X-shape, or any of other suitableshape. The inner tube 224 has an inner liquid guide surface 226f held inintimate contact with the resilient seal rings 235. The inner tube 224has a plurality of radially through liquid supply ports 226c open at theinner liquid guide surface 226f, confronting the initial pressurizingregion 225a-1 and communicating with the pressure chamber 228. Asuitable number of liquid supply and discharge ports 226g extendradially through the inner tube 224 adjacent the upper end of the liquidguide surface 226f and in communication with the pressure chamber 228,the liquid supply and discharge ports 226g radially confronting the lid3 through the pressure tube 225. A suitable number of liquid supply anddischarge ports 226h are also defined radially through the inner tube224 adjacent the lower end of the liquid guide surface 226 f and incommunication with the pressure chamber 228, the liquid supply anddischarge ports 226h radially confronting the lid 4 through the pressuretube 225. The upper and lower liquid supply and discharge ports 226g,226h are provided to discharge air present between the liquid guidesurface 226f and the pressure tube 225, and are normally closed off bythe outer peripheral surface 225a of the pressure tube 225. Portions225c, 225d of the pressure tube 225 which close the liquid supply anddischarge ports 226g, 226h are radially backed by the lids 3, 4 of thepressed assembly 21, so that the liquid supply and discharge ports 226g,226h remain closed until these portions 225c, 225d are flexibly deformed(FIG. 17). The outer tube 223 has liquid supply and discharge ports223a, 223b defined in the vicinity of upper and lower ends thereof andopen to the pressure chamber 228. The liquid supply and discharge ports223a, 223b are coupled to liquid supply and discharge pipes of a liquidsupply and discharge system (not shown).

The number of the pressurizing regions on the outer peripheral surface225a of the pressure tube 225 is not limited to seven, but two or morepressurizing regions may be defined. The initial pressurizing region isnot limited to the central pressurizing region 225a-1, but the mostsuitable pressurizing region may be selected according to thethree-dimensional shape of the product to be formed.

In the apparatus 220 of the illustrated embodiment, the longitudinalaxis of the powder filling space 1 is shown as extending vertically.However, the longitudinal axis of the powder filling space 1 may beinclined or horizontal.

The operation of the apparatus 220, or a method according to the presentinvention, will be described below. As shown in FIGS. 14 and 15, thepressed assembly 21 is provided with a mass of powder 14 in the powderfilling space 1. The pressed assembly 21 is then inserted into thepressing assembly 222, and held in position by upper and lower clamps12, 13 threaded in the pressing assemblY 222. Then, a pressurizingliquid 7 (such as oil, glycerin, an aqueous solution of boric acid, orthe like) which is supplied under pressure from the liquid supply anddischarge system flows through the liquid supply and discharge ports223a, 223b of the outer tube 223 into the pressure chamber 228. When thepressure of the liquid 7 in the pressure chamber 228 reaches aprescribed level (for example in the range of 50 to 200 kg/cm²), theliquid 7 flows through the liquid supply ports 226c toward the pressuretube 225 and between the initial pressurizing region 225a-1 of thepressure tube 225 and the liquid guide surface 226f. Since the liquidsupply and discharge ports 226g, 226h defined adjacent the upper andlower ends of the inner tube 224 are closed by the portions 225c, 225dof the pressure tube 225, the liquid 7 under pressure does not flow outpast the pressure tube 225. As shown in FIG. 16(A), the liquid 7 thathas flowed to the initial pressurizing region 225a-1 only presses theapparatus at the same to elastically expand it radially inwardly, sincethe upper and lower ends of the initial pressurizing region 225a-1 arelimited by the resilient seal rings 235. The mold 2 is now pressed onlyat a portion of its outer peripheral surface 2a which faces the initialpressurizing region 225a-1, compacting the powder 14. Air (not shown) inthe pressurized powder 14 is increased in pressure and quickly flowsinto air passages defined by gaps between powder particles which are notcompacted. Therefore, no air remains under compression in thepressurized powder 14. As the amount of supplied liquid 7 increases, theinitial pressurizing region 225a-1 is more flexed. As shown in FIG.16(B), the annular grooves 225b defined on opposite sides of the initialpressurizing region 225a-1 are deformed radially inwardly, reducing theannular groove inside diameter A. As the annular groove inside diameterA decreases, the outside diameter B of the resilient seal rings 235fitted in the respective annular grooves 225b with an interference fitis reduced to develop a gap between the seal rings 235 and the liquidguide surface 226f, whereupon the sealing ability of the seal rings 235is lost. When the sealing ability of the seal rings 235 is lost, theliquid 7 flows into the pressurizing regions 225a-2, 225a-3 adjacent tothe initial pressurizing regions 225a-1 and presses these pressurizingregions 225a-2, 225a-3. The mold 2 is now pressed at portions of itsouter peripheral surface 2a positioned in facing relation to thepressurizing regions 225a-2, 225a-3, thereby compacting the powder 14.Air (not shown) in the compacted powder 14 is increased in pressure andquickly flows into air passages defined by gaps between powder particleswhich are not yet compacted. Therefore, no air remains under pressure inthe pressurized powder 14. As the amount of supplied liquid 7 becomesgreater, the liquid 7 progressively presses the pressurizing regions225a-4, 225a-5 and then the pressurizing regions 225a-6, 225a-7 in thesame manner as described above, as shown in FIG. 17. In response to suchprogressive pressurization of the pressure tube 225, the powder 14filled in the powder filling space 1 is progressively compacted from theregion in the powder filling space 1 which confronts the initialpressurizing region 225a-1 toward the ends 1a, 1b of the powder fillingspace 1. As the powder 14 is axially progressively pressurized orcompacted, air present in the powder 14 in the powder filling space 1 issqueezed from the region in the powder filling space 1 which confrontsthe initial pressurizing region 225a-1 toward the ends 1a, 1b of thepowder filling space 1, and is finally discharged out of the powderfilling space 1 through the thread gaps defined between the boltportions 9a, 9b of the core 9 and the nuts 10, 11. Consequently, airunder pressure which would damage a formed product is prevented frombeing trapped in the compacted powder 14. The liquid 7 under pressuresupplied between the entire outer peripheral surface 225a and the liquidguide surface 226f is pressurized up to a prescribed final pressurelevel (for example, in the range of 500 to 5,000 kg/cm²), to compact thepowder 14. After pressurization is performed over a prescribed period oftime, the pressure of the liquid 7 in the pressure chamber 228 isreduced. As the pressure of the liquid 7 is lowered, the flexible mold 2and the pressure tube 225 return to their original shape under their ownresiliency until the original inside diameter D of the mold 2 isrecovered, as shown in FIG. 18. After the upper clamp 12 has beendetached from the retainer case 226, the pressed assembly 21 is pulledout of the retainer case 226. Then, the nuts 10, 11 and the lids 3, 4are removed, and the formed product 234 and the core 9 are separatedfrom each other.

7th Embodiment

FIG. 19 shows an apparatus 240 according to a seventh embodiment of thepresent invention. The apparatus 240 is most significantly differentfrom the sixth embodiment (FIG. 4) in that a retainer case 36 is similarto that of the third embodiment (FIG. 7), no mold is provided, and aninner surface 245j of a pressure tube 245 serves as a powder compactingsurface.

8th Embodiment

FIGS. 20 through 24 show an apparatus 320 according to an eighthembodiment of the present invention, the apparatus 320 comprising apressed assembly 21 and a pressing assembly 322. The pressed assembly 21has the same structure as that of the first embodiment (FIG. 1).

As shown in FIG. 20, the pressing assembly 322 having an improvedstructure includes a pressure tube 325 fitted in a retainer case 326.The retainer case 326 comprises a rigid outer tube 323, an inner tube324 backing the pressure tube 325, and a pair of upper and lower lids331, 332 threaded over the upper and lower ends, respectively, of theouter tube 323 and sandwiching the pressure tube 325. An annularpressure chamber 338 is defined between the outer tube 323 and the innertube 324. The pressure tube 325 is made of a flexible material such asneoprene rubber, urethane resin, or the like and has a core layer 327covered with a covering layer 328. The core layer 327 comprises an arrayof separate ring members 327a, 327b, 327c, 327d held in endwise abutmentand each having a length L in the range of 100 to 300 mm, for example.The ring members 327a, 327b, 327b, 327d have moduli of elasticity thatare progressively greater from the central ring member 327a to the ringsclosest to the open ends 1a, 1b of the powder filling space 1. To obtaina desired Young's modulus, the rubber hardness of the ring members 327a,327b, 327c, 327d may be selected in the JIS rubber hardness range of 40to 90, for example. The pressure tube 325 is not limited to theillustrated structure, but may comprise only the core layer 327. Thepressure tube 325 has seven pressurizing regions 325-1, 325-2, ...325-7, the central pressurizing region 325-1 serving as an intialpressurizing region. The inner tube 324 has an inner liquid guidesurface 326f held in intimate contact with the outer peripheral surface325a of the pressure tube 325. The inner tube 324 has a plurality ofradially extending liquid supply ports 326c open at the inner liquidguide surface 326f, in confronting the initial pressurizing region 325-1and communicating with the pressure chamber 338. A suitable number ofliquid supply and discharge ports 326g extend radially through the innertube 324 adjacent the upper end of the liquid guide surface 326f and incommunication with the pressure chamber 338, the liquid supply anddischarge ports 326g radially confronting the lid 3 through the pressuretube 325. A suitable number of liquid supply and discharge ports 326halso extend radially through the inner tube 324 adjacent the lower endof the liquid guide surface 326f and in communication with the pressurechamber 338, the liquid supply and discharge ports 326h radiallyconfronting the lid 4 through the pressure tube 325. The upper and lowerliquid supply and discharge ports 326g, 326h are provided to dischargeair present between the liquid guide surface 326f and the pressure tube325, and are normally closed off by the outer peripheral surface 325a ofthe pressure tube 325. Portions 325c, 325d of the pressure tube 325which close the liquid supply and discharge ports 326g, 326h areradially backed by the lids 3, 4 of the pressed assembly 21, so that theliquid supply and discharge ports 326g, 326h remain closed until theseportions 325c, 325d are flexibly deformed (FIG. 23). The outer tube 323has liquid supply and discharge ports 323a, 323b defined in the vicinityof upper and lower ends thereof and open to the pressure chamber 338.The liquid supply and discharge ports 323a, 323b are coupled to liquidsupply and discharge pipes of a liquid supply and discharge system (notshown).

The number of the pressurizing regions of the pressure tube 325 is notlimited to seven, but two or more pressurizing regions may be defined.The initial pressurizing region is not limted to the centralpressurizing region 325-1, but any number of plural pressurizing regionsmay be selected.

In the apparatus 320 of the illustrated embodiment, the longitudinalaxis of the powder filling space 1 is shown as extending vertically.However, the longitudinal axis of the powder filling space 1 may beinclined or horizontal.

The operation of the apparatus 320, or a method according to the presentinvention, will be described below. As shown in FIGS. 20 and 21, thepressed assembly 21 is provided with a mass of powder 14 in the powderfilling space 1. The pressed assembly 21 is then inserted into thepressing assembly 322, and is held in position by upper and lower clamps12, 13 threaded in the pressing assembly 322. Then, a pressurizingliquid 7 (such as oil, glycerin, an aqueous solution of boric acid orthe like) which is supplied under pressure from the liquid supply anddischarge system flows through the liquid supply and discharge ports323a, 323b of the outer tube 323 into the pressure chamber 338. When thepressure of the liquid 7 in the pressure chamber 338 reaches aprescribed level (for example in the range of from 50 to 200 kg/cm²),the liquid 7 flows through the liquid supply ports 326c toward thepressure tube 325 and enters between the initial pressurizing region325-1 of the pressure tube 325 and the liquid guide surface 326f. Sincethe liquid supply and discharge ports 326g, 326h defined closely to theupper and lower ends of the inner tube 324 are closed by the portions325c, 325d of the pressure tube 325, the liquid 7 under pressure doesnot flow out past the pressure tube 325. As shown in FIG. 22(A), theliquid 7 flowed to the initial pressurizing region 325-1 first pressesthe same to elastically expands it radially inwardly, since the modulusof elasticity of the initial pressurizing region 325-1 is smaller thanthose of the pressurizing regions 325-2, 325-3, and hence the initialpressurizing region 325-1 is deformed more easily. The mold 2 is nowpressed only at a portion of its outer peripheral surface 2a which facesthe initial pressurizing region 325-1, compacting the powder 14. Air(not shown) in the pressurized powder 14 is increased in pressure andquickly flows into air passages defined by gaps between powder particleswhich are not compacted. Therefore, no air remains under compression inthe pressurized powder 14. As the amount of supplied liquid 7 increases,the initial pressurizing region 325-1 is more flexed, and, as shown inFIG. 22(B), the liquid 7 flows into the pressurizing regions 325-2,325-3 adjacent the initial pressurizing regions 325-1 and presses thesepressurizing regions 325-2, 325-3. The mold 2 is now pressed at portionsof its outer peripheral surface 2a which face the pressurizing regions325-2, 325-3, thereby compacting the powder 14. The pressure of air (notshown) in the compacted powder 14 is increased and the air quickly flowsinto air passages defined by gaps between powder particles which are notyet compacted. Therefore, no air remains under pressure in thepressurized powder 14. The pressure of the liquid 7 is larger when thepressurizing regions 325-2, 325-3 are pressed than when the initialpressurizing region 325-1 are pressed. As the pressurizing force isincreased, the powder 14 which has initially been compacted in theregion of the powder filling space 1 confronting the initialpressurizing region 325-1 is further pressurized. The increasedpressurizing force is also effective to discharge a small amount ofcompressed air remaining in the powder 14, thus fully removingcompressed air from the powder 14. As the pressure of supplied liquid 7becomes greater, the liquid 7 progressively presses the pressurizingregions 325-4, 325-5 and then the pressurizing regions 325-6, 325-7 inthe same manner as described above, as shown in FIG. 23. In response tosuch progressive pressurization of the pressure tube 325, the powder 14in the powder filling space 1 is progressively compacted from the regionin the powder filling space 1 which confronts the initial pressurizingregion 325-1 toward the ends 1a, 1b of the powder filling space 1. Asthe powder 14 is axially progressively pressurized or compacted, airpresent in the powder 14 filled in the powder filling space 1 issqueezed from the region in the powder filling space 1 which confrontsthe initial pressurizing region 325-1 toward the ends 1a, 1b of thepowder filling space 1, and is finally discharged out of the powderfilling space 1 through the thread gaps defined between the boltportions 9a, 9b of the core 9 and the nuts 10, 11. Consequently, airunder pressure which would damage a formed product is prevented frombeing trapped in the compacted powder 14. The liquid 7 under pressuresupplied between the entire outer peripheral surface 325a and the liquidguide surface 326f is pressurized up to a prescribed final pressurelevel (for example, in the range of 500 to 5,000 kg/cm²) to compact thepowder 14. After pressurization is performed over a prescribed period oftime, the pressure of the liquid 7 in the pressure chamber 338 isreduced. As the pressure of the liquid 7 is lowered, the flexible mold 2and the pressure tube 325 return to their original shape under their ownresiliency until the original inside diameter D of the mold 2 isrecovered, as shown in FIG. 24. After the upper clamp 12 has beendetached from the retainer case 326, the pressed assembly 21 is pulledout of the retainer case 326. Then, the nuts 10, 11 and the lids 3, 4are removed, and the formed product 339 and the core 9 are separatedfrom each other.

9th Embodiment

FIG. 25 shows an apparatus 340 according to a ninth embodiment of thepresent invention. The apparatus 340 differs from the apparatus 320 ofthe eighth embodiment (FIG. 20) with respect to the structure of aretainer case 346, seal structures 381, 382 near the upper and lowerends of the pressure tube 325, and in that a protective tube 377 isinterposed between the pressure tube 325 and the mold 2.

The retainer case 346 comprises a rigid outer tube 343 and two lids 344,345 threaded to the outer tube 343 in upper and lower openings,respectively, thereof. The pressure tube 325 is fitted in the retainercase 346 which has a liquid guide surface 346f defined on the outer tube343 confronting the outer peripheral surface 325a of the pressure tube325. The liquid guide surface 346f has an annular distribution groove343d confronting the intial pressurizing region 325-1 of the pressuretube 325, an annular distribution groove 343e confronting the upperpressurizing region 325-6, and an annular distribution groove 343fconfronting the lower pressurizing region 325-7. The outer tube 343 hasliquid supply and discharge ports 343c, 343a, 343b defined therein andcommunicating, respectively, with the annular distribution grooves 343d,343e, 343f. After the pressurizing liquid 7 fills the space between theliquid guide surface 346f and the pressure tube 325, it is supplied fromthe central liquid supply and discharge port 343c and discharged fromthe upper and lower liquid supply and discharge ports 343a, 343b toremove air completely.

The protective tube 377 is made of a flexible material such as neoprenerubber, urethane resin, or the like. The protective tube 377 protectsthe pressure tube 325 by holding the pressure tube 325 out of contactwith the lids 3, 4 of the pressed assembly 21.

As shown in FIG. 26, the seal structure 381 near the upper end of thepressure tube 325 includes an annular groove 385 defined in a lid 344.The pressure tube 325 has an upper edge 325e extending in the annulargroove 385 and having an outer peripheral surface 325a with a seal ringgroove 386 defined therein. A seal ring 387 extending in the seal ringgroove 386 is held in intimate contact with the inner peripheral surface385a of the annular groove 385. The annular groove 385 has an innermostsurface 385b serving as a backup portion for the upper edge 325e of thepressure tube 325. The cross section of the seal ring 387 is not limitedto an 0-shape, but may be a V-shape, an X-shape, or any of othersuitable shape. The seal structure 382 (FIG. 25) near the lower end ofthe pressure tube 325 is identical to the seal structure 381 near theupper end.

FIGS. 27(A) and 27(B) illustrate another seal structure which may bedisposed near each of the upper and lower ends of the pressure tube 325.The seal structure 391 includes an annular groove 385 defined in a lid344. The pressure tube 325 has an upper edge 325e extending in theannular groove 385 which has an inner peripheral surface 385a with aseal ring groove 396 defined therein. A seal ring 397 extending in theseal ring groove 396 is held in intimate contact with the upper edge325e of the pressure tube 325. The annular groove 385 has an innermostsurface 385b serving as a backup portion for the upper edge 325e of thepressure tube 325.

FIGS. 28(A) and 28(B) show still another seal structure which may bedisposed near each of the upper and lower ends of the pressure tube 325.The seal structure 401 includes an annular groove 385 defined in a lid344. The pressure tube 325 has an upper edge 325e extending in theannular groove 385. Two confronting seal ring grooves 408, 409 aredefined, respectively, in the outer peripheral surface 325a of the upperedge 325e and the inner peripheral surface 385a of the annular groove385. A seal ring 407 disposed in the seal ring grooves 408, 409 is heldin intimate contact with the bottoms 408a, 409a of the seal ring grooves408, 409. The annular groove 385 has an innermost surface 385b servingas a backup portion for the upper edge 325e of the pressure tube 325.

10th Embodiment

FIG. 29 shows an apparatus 410 according to a tenth embodiment of thepresent invention. The apparatus 410 is different from the apparatus 340(FIG. 25) of the ninth embodiment in that a mold and a protective tubeare not provided, and the inner surface 325'j of a pressure tube 325'serves as a powder compacting surface.

11th Embodiment

FIGS. 30 through 35 illustrate an apparatus 440 according to an eleventhembodiment of the present invention. The apparatus 440 is mostsignificantly different from the apparatus 220 (FIG. 14) of the sixthembodiment in that a backup tube 457 is interposed between a pressuretube 225 retained by a retainer case 456 and a mold 2. The backup tube457 is made of a flexible material such as neoprene rubber, urethaneresin, or the like and has a modulus of elasticity that becomesprogressively greater from its region confronting the initialpressurizing region 225a-1 on the outer peripheral surface 225a of thepressure tube 225 to its regions closest to the open ends 1a, 1b of thepowder filling space 1. As shown in FIG. 30, the backup tube 457comprises an array of separate ring members 457a, 457b, 457c, 457d heldin endwise abutment and having different moduli of elasticity. To obtaina desired modulus of elasticity, the rubber hardness of the ring members457a, 457b, 457c, 457d may be selected in the JIS rubber hardness rangeof 40 to 90, for example. As shown in FIG. 32, the array of separatering members 457a, 457b, 457c, 457d having different moduli ofelasticity may be covered with inner and outer flexible layers 457h,457i. The backup tube 457 is not limited to the illustrated structurewith its modulus of elasticity varying in a stepwise manner, but themodulus of elasticity of the backup tube 457 may continuously increasefrom the region confronting the initial pressurizing region 225a-1 onthe pressure tube 225 to the regions closest to the open ends 1a, 1b ofthe powder filling space 1.

The operation of the apparatus 440, or a method according to the presentinvention, will be described below. As shown in FIGS. 30 and 31, thepressed assembly 21 with the powder 14 in the powder filling space 1 isinserted into the pressing assembly 422. When the pressure of thepressurizing liquid 7 supplied to a pressure chamber 428 reaches aprescribed pressure level (for example in the range of 50 to 200kg/cm²), the liquid 7 flows out through liquid supply ports 456c andbetween the initial pressurizing region 225a-1 of the pressure tube 225and a liquid guide surface 456f of the retainer case 456. Since liquidsupply and discharge ports 456g, 456h defined adjacent the upper andlower ends of an inner tube 424 are closed by annular portions 429a,430a of lids 429, 430, the liquid 7 under pressure does not flow outpast the pressure tube 225. As shown in FIG. 33(A), the liquid 7 thathas flowed to the initial pressurizing region 225a-1 first presses thepressed assembly at only the same to elastically expand it radiallyinwardly, since the the upper and lower ends of the initial pressurizingregion 225a-1 are limited by the resilient seal rings 235. The mold 2 isnow pressed only at a portion of its outer peripheral surface 2a whichfaces the initial pressurizing region 225a-1, compacting the powder 14.The pressure of air (not shown) in the pressurized powder 14 isincreased and the air quickly flows into air passages defined by gapsbetween powder particles which are not compacted. Therefore, no airremains under pressure in the pressurized powder 14. As the amount ofsupplied liquid 7 increases, the pressure tube 225 of the initialpressurizing region 225a-1 and the region of the backup tube 457 whichconfronts the initial pressuring region 225a-1 are flexed more. As theseregions are flexed more, the pressurizing liquid 7 flows into thepressurizing regions 225a-2, 225a-3 adjacent the initial pressurizingregion and presses these pressurizing regions 225a-2, 225a-3. The mold 2is now pressed at portions of its outer peripheral surface 2a which facethe pressurizing regions 225a-2, 225a-3, thereby compacting the powder14. The pressure of air (not shown) in the compacted powder 14 isincreased and the air quickly flows into air passages defined by gapsbetween powder particles which are not yet compacted. Therefore, no airremains under pressure in the pressurized powder 14. The pressure of theliquid 7 which presses the pressurizing regions 225a-2, 225a-3 is largerthan when pressing the initial pressurizing region 225a-1 only since themodulus of elasticity of the ring members 457b is larger than that ofthe ring member 457a. As the pressurizing force is increased, the powder14 which has initially been compacted in the region of the powderfilling space 1 confronting the initial pressurizing region 225a-1 isfurther pressurized. The increased pressurizing force is also effectiveto discharge a small amount of compressed air remaining in the powder14, thus fully removing compressed air from the powder 14. As thepressure of supplied liquid 7 becomes greater, the liquid 7progressively presses the pressurizing regions 225a-4, 225a-5 and thenthe pressurizing regions 225a-6, 225a-7 in the same manner as describedabove, as shown in FIG. 34. In response to the progressivepressurization of the pressure tube 225, the powder 14 in the powderfilling space 1 is progressively compacted from the region in the powderfilling space 1 which confronts the initial pressurizing region 225a-1toward the ends 1a, 1b of the powder filling space 1. As the powder 14is axially progressively pressurized or compacted, air present in thepowder 14 in the powder filling space 1 is squeezed from the region inthe powder filling space 1 which confronts the initial pressurizingregion 225a-1 toward the ends 1a, 1b of the powder filling space 1, andis finally discharged out of the powder filling space 1 through thethread gaps defined between the bolt portions 9a, 9b of the core 9 andthe nuts 10, 11. Consequently, air under pressure which would damage aformed product is prevented from being trapped in the compacted powder14. The liquid 7 under pressure supplied between the entire outerperipheral surface 225a and the liquid guide surface 456f is pressurizedup to a prescribed final pressure level (for example, in the range of500 to 5,000 kg/cm²) to compact the powder 14. After pressurization isperformed over a prescribed period of time, the pressure of the liquid 7in the pressure chamber 428 is reduced. As the pressure of the liquid 7is lowered, the flexible mold 2, the backup tube 457, and the pressuretube 225 return to their original shape under their own resiliency untilthe original inside diameter D of the mold 2 is recovered, as shown inFIG. 35. After the upper clamp 12 has been detached from the retainercase 456, the pressed assembly 21 is pulled out of the retainer case456, and a formed product 459 is separated.

12th Embodiment

FIG. 36 shows an apparatus 470 according to a twelfth embodiment of thepresent invention. The apparatus 470 differs from the apparatus 440 ofthe eleventh embodiment (FIGS. 30 and 34) with respect to the structureof a retainer case 476, seal structures 481, 482 near the upper andlower ends of the pressure tube 225, and in that a protective tube 477is interposed between the backup tube 457 and the mold 2.

The protective tube 477 is made of a flexible material such as neoprenerubber, urethane resin, or the like. The protective tube 477 protectsthe backup tube 457 by holding the backup tube 457 out of contact withthe lids 3, 4 of the pressed assembly 21.

The retainer case 476 comprises a rigid outer tube 473 and two lids 479,480 threaded in upper and lower openings, respectively, of the outertube 473. The pressure tube 225 is fitted in the retainer case 476 whichhas a liquid guide surface 476f defined on the outer tube 473 inconfronting relation to the outer peripheral surface 225a of thepressure tube 225. The liquid guide surface 476f has an annulardistribution groove 473d confronting the intial pressurizing region225a-1 of the pressure tube 225, an annular distribution groove 473econfronting the upper pressurizing region 225a-6, and an annulardistribution groove 473f confronting the lower pressurizing region225a-7. The outer tube 473 has liquid supply and discharge ports 473c,473a, 473b defined therein and communicating respectively with theannular distribution grooves 473d, 473e, 473f. After the pressurizingliquid 7 fills the space between the liquid guide surface 476f and thepressure tube 225, it is supplied from the central liquid supply anddischarge port 473 c and discharged from the upper and lower liquidsupply and discharge ports 473a, 473b to remove air completely.

The seal structures 481, 482 near the upper and lower ends of thepressure tube 225 are identical to the seal structures 81, 82 of thethird embodiment (FIGS. 7 and 8), the seal structure 91 (FIGS. 9(A) and9(B)), or the seal structure 101 (FIGS. 10(A) and 10(B)).

13th Embodiment

FIG. 37 shows an apparatus 510 according to a thirteenth embodiment ofthe present invention. The apparatus 510 is different from the apparatus470 (FIG. 36) of the twelfth embodiment in that a mold and a protectivetube are not provided, and the inner surface 457j of an inner layer 457hof the backup tube 457 serves as a powder compacting surface.

(14th Embodiment)

FIGS. 38 and 39 illustrate an apparatus 520 according to a fourteenthembodiment of the present invention. The apparatus 520 comprises apressed assembly 521 and a pressing assembly 522.

As shown in FIG. 38, the pressing assembly 522 comprises a flexiblepressure tube 525 disposed in a retainer case 526. The pressure tube 525is composed of seven independent short tubes 527 which are axiallycoupled. The short tubes 527 have annular pressure chambers 529-1,529-2, ..., 529-7 defined around their respective tube walls 527a. Asshown in FIG. 39, a partition 528 projecting from the inner peripheralsurface of the retainer case 526 may be interposed between adjacentshort tubes 527 for preventing the pressure in a pressure chamber frombeing transmitted into adjacent pressure chambers. The retainer case 526has fluid supply ports 526c defined therein at radial positionscorresponding to the pressure chambers 529-1, 529-2, ..., 529-3,respectively. At least one fluid supply port is associated with each ofthe pressure chambers. The pressure tube 525 is not limited to theillustrated structure of coupled independent short tubes 527, but mayhave a unitary construction having a plurality of annular pressurechambers defined around a tube wall.

The pressed assembly 521 comprises a flexible mold 532 with a powderfilling space 1 defined therein, a pair of lids 533, 534 closing upperand lower open ends 1a, 1b, respectively, of the powder filling space 1,and a core 539 extending between the upper and lower lids 533, 534, ifdesired.

The operation of the apparatus 520, or a method according to the presentinvention, will be described hereinbelow. The pressed assembly 521 isprovided with powder 14 in the powder filling space 1. The pressedassembly 521 is then inserted into the pressure tube 525 of the pressingassembly 522, and pressurized by a pressurizing fluid 537 introducedinto the pressure chambers 529-1, 529-2, ..., 529-7.

The pressurizing process will be described in detail with reference toFIG. 40. The pressurizing fluid 537 such as air, oil, glycerin, or thelike is introduced into the pressure chambers 529-1, 529-2, ..., 529-7under a low initial pressure P1 in the range of 1 to 10 kg/cm², forexample (see FIG. 40 at (a)), and the pressurizing fluid 537 is keptunder such a low pressure for a suitable period of time. Then, thepressurizing fluid 537 under a maximum pressure P2 (see FIG. 40 at (b))in the range of 15 to 30 kg/cm², for example, is introduced into thecentral pressure chamber 529-4, and the pressurizing fluid 537 in thepressure chamber 529-4 is maintained in this state for a suitable periodof time. Then, the pressurizing fluid 537 under the maximum pressure P2is introduced into the pressure chambers 529-3, 529-5 and thepressurizing fluid 537 in the pressure chambers 529-3, 529-5 ismaintained in this state for a suitable period of time. In this manner,the pressurizing fluid 537 under the maximum pressure is progressivelyintroduced toward the pressure chambers 529-1, 529-7 at the upper andlower ends (see FIG. 40 at (c) and (d)). The progressive introduction ofthe maximum fluid pressure serves to squeeze air in the powder 14 fromthe central region of the powder filling space 1 toward the upper andlower ends 1a, 1b thereof. After the maximum fluid pressure P2 has beensupplied to the pressure chambers 529-1, 529-7 at the upper and lowerends, the maximum fluid pressure P2 is maintained for an appropriateperiod of time. Thereafter, the fluid pressure is removed from thepressure chambers 529-1, 529-2, ..., 529-7. Finally, the pressedassembly 521 is taken out of the pressing assembly 522, and a formedproduct (not shown), the core 539, and the mold 532 are separated fromeach other.

The pressurizing process is not limited to the above-described pattern,but may be modified depending on the three-dimensional shape of aproduct to be formed, as follows:

Only one pressure chamber into which the maximum fluid pressure P2 is tobe introduced first is selected from the pressure chambers 529-1, 529-2,..., 529-7. The maximum fluid pressure is progressively introducedtoward the pressure chamber 529-1 and/or the pressure chamber 529-7positioned at the end.

The initial compaction of the powder may be effected by a two-steppressurization process involving pressurization under a relatively lowfluid pressure and pressurization under a relatively high fluidpressure.

The initial compaction of the powder may be carried out by firstintroducing the initial fluid pressure Pl into a selected one of thepressure chambers 529-1, 529-2, ..., 529-7, and then progressivelyapplying the fluid pressure toward the the pressure chamber 529-1 and/orthe pressure chamber 529-7 positioned at the end. In this case, thepowder compaction under the maximum fluid pressure P2 may be effected bypressurizing all of the pressure chambers at the same time.

Further, the initial compaction under the initial low fluid pressure Plmay be omitted, and the powder may be compacted by progressivelyapplying only the maximum fluid pressure P2.

Other Embodiments

In the aforesaid embodiments, the inner peripheral surface 2j of themold 2 (FIG. 1), the inner peripheral surface 121j of the mold 121 (FIG.13), the inner peripheral surface 532j of the mold 532 (FIG. 38), theinner peripheral surface 117j of the pressure tube 117 (FIG. 11), theinner peripheral surface 245j of the pressure tube 245 (FIG. 19), theinner peripheral surface 325'j of the pressure tube 325' (FIG. 29), andthe inner peripheral surface 457j of the backup tube 457 (FIG. 37),which serve as powder compacting surfaces, are cylindrical surfaces forproducing hollow or solid cylindrical products. However, the shape of aproduct that can be produced by the apparatus of the invention is norlimited to a cylindrical shape. Instead, inner surfaces having variousshapes may be employed as powder compacting surfaces to form productshaving three-dimensional shapes Moreover, in the above-describedembodiments, the pressure tube 25 (FIG. 1), the pressure tube 75 (FIG.7), the pressure tube 117 (FIG. 11), and the pressure tube 127 (FIG. 13)have a cylindrical shape. However, the outer surfaces of the pressuretubes are not limited to being cylindrical, but may have variousconfigurations to generate pressurizing forces sufficient to formproducts having three-dimensional shapes.

The present invention offers the following advantages:

(1) Since air in a mass of powder filled in a powder filling space canbe squeezed toward the ends of the powder filling space where the airdoes not adversely affect a formed product, no compressed air will betrapped in the powder.

(2) Inasmuch as the powder and air can be completely separated from eachother, the formed product is not damaged when it is removed from themold.

(3) In an experiment conducted by the inventor, ceramic powder wascompacted by the apparatus of the invention to form a hollow producthaving an outside diameter of 300 mm, an inside diameter of 240 mm, anda length of 4,000 mm. The experiment clearly indicates that theapparatus of the present invention is capable of producing elongateproducts which have not been possible heretofore.

Although certain preferred embodiments have been shown and described, itshould be understood that many changes and modifications may be madetherein without departing from the scope of the appended claims.

We claim:
 1. A dry-type rubber pressing apparatus comprising:a flexibletube having a powder-receiving space defined therein, and an outerperipheral surface having a plurality of annular grooves extendingtherein, said grooves spaced from one another axially along said tube; aplurality of resilient rings respectively disposed in said grooves in aninterference fit with said flexible tube; a retainer case disposed oversaid flexible tube, said retainer case having a liquid-guiding surfacein direct contact with each of said resilient rings, a plurality ofpressurizing regions being radially defined between the outer peripheralsurface of said flexible tube and the liquid-guiding surface of saidretainer case and being axially defined by said annular grooves,respectively, one of said pressurizing regions being an initialpressurizing region at which liquid is initially introduced to saidpressurizing regions, and said retainer case having a liquid supply portopen at said liquid-guiding surface to said initial pressurizing regionfor allowing liquid to be introduced therethrough to said initialpressurizing region, said flexible tube being flexible to a degree atwhich, while liquid is introduced to said initial pressurizing regionthrough said supply port the respective portion of said flexible tubedefining said initial pressurizing region deforms with contact beingmaintained between each said seal ring at which said initialpressurizing region terminates and said liquid-guiding surface, and atwhich once liquid introduced to said initial pressurizing region reachesa predetermined pressure said flexible tube further deforms in a mannerin which each said seal ring at which said initial pressurizing regionterminates is moved out of contact with said liquid guiding-surface. 2.A dry-type rubber pressing apparatus comprising:a flexible tube having apowder-receiving space defined therein, and an outer peripheral surfacehaving a plurality of annular grooves extending therein, said groovesspaced from one another axially along said tube; a plurality ofresilient rings respectively disposed in said grooves in an interferencefit with said flexible tube; a retainer case disposed over said flexibletube, said retainer case having a liquid-guiding surface in directcontact with each of said resilient rings, a plurality of pressurizingregions being radially defined between the outer peripheral surface ofsaid flexible tube and the liquid-guiding surface of said retainer caseand being axially defined by said annular grooves, respectively, one ofsaid pressurizing regions being an initial pressurizing region at whichliquid is initially introduced to said pressurizing regions, and saidretainer case having a liquid supply port open at said liquid-guidingsurface to said initial pressurizing region for allowing liquid to beintroduced therethrough to said initial pressurizing region; and aflexible pressure-transmitting means disposed in said flexible pressuretube, said flexible pressure-transmitting means having the shape of atube with an outer peripheral surface and opposite ends, a local portionradially aligned with said initial pressurizing region, and a modulus ofelasticity that increases as taken axially from said local portiontoward one of said opposite ends.
 3. A dry-type rubber pressingapparatus as claimed in claim 2,wherein said flexible tube and saidflexible pressure-transmitting means are integral.
 4. A dry-type rubberpressing apparatus as claimed in claim 1,and further comprising aflexible mold disposed within said flexible tube.
 5. A dry-type rubberpressing apparatus as claimed in claim 2,and further comprising aflexible mold disposed within said flexible pressure-transmitting means.6. A dry-type rubber pressing apparatus as claimed in claim 3,andfurther comprising a flexible mold disposed within said flexiblepressure-transmitting means.
 7. A dry-type rubber pressing apparatus asclaimed in any one of claims 1, 2-4, 5 and 6,and further comprising acore extending axially within said powder-receiving space.